Wilson . — Spermatogenesis in the Bryophyta . 427 
it is sometimes found in an almost diagonal position. Even in these cases 
the resulting daughter-cells are rarely triangular in section, for the division 
wall does not usually strike the mother-cell wall at the intersection of two 
of its sides. The spindle is not well marked, and no centrosomes are 
found at the poles. The number of chromosomes present can be clearly 
seen both in polar (Fig. 12) and in side views (Fig. 11) ; six are constantly 
found. 
Separation goes on in the usual way, and during the anaphase the 
daughter chromosomes can be distinguished on account of the small number 
present (Fig. 13). In polar view six can be again clearly seen (Fig. 14). On 
their arrival at the poles the chromosomes lose their sharp outlines, and on 
the appearance of the nuclear membrane can no longer be distinguished 
(Fig. 15). In the figure of this stage given by J. and W. Docters van 
Feeuwen-Reijnvaan distinct chromosomes are shown inside the daughter 
nuclei, but in the present investigation no such appearance has been seen. 
The reduction in number of chromosomes described by these investigators 
does not take place in Mnium hornum . 
During the later stages of the final division vacuoles frequently appear 
in the cytoplasm, and these often persist in the daughter nuclei. The 
division wall arises in the usual way, but at a comparatively late period. 
The daughter nuclei at first contain several deeply staining granules, but 
later these are replaced by a single centrally placed nucleolus. 
The cells after the final division is completed are somewhat irregular in 
shape, generally four or five sided, and at first occupy the whole cavity. 
But very shortly a shrinkage takes place, the protoplasm contracts from the 
wall, and the cell becomes rounded. The resulting spermatid is oval in 
form (Fig. 16). The nucleus is large and possesses a single centrally placed 
nucleolus, while the remaining part is made up of a fine network which con- 
tains little or no chromatin. The cytoplasm is finely alveolar, and one or 
more large vacuoles are usually found in it ; no deeply staining granules can 
be distinguished. The original walls of the cells remain thin and sharply 
defined, and stain readily with orange G or Flemming’s triple stain. 
The nucleolus soon becomes slightly elongated and constricts in the 
middle, dividing into two bodies of almost equal size which at first remain 
in close contact (Fig. 17). The process is then repeated in one of the two 
resultant bodies, so that three are now found placed in a row within the 
nucleus. The nuclear membrane, which up to this time has been sharply 
defined, now loses its distinctness, and in consequence the limits of the 
nucleus can only be distinguished with difficulty. A separation of the 
bodies within the nucleus now takes place, and two of them pass into 
the cytoplasm. 
Although the sequence of events just described is by far the most 
common, several variations of it may occur. In some cases it appears that 
